1. Technical Field
This invention generally relates to musical apparatus. In particular the invention pertains to an apparatus for determining a tonality from a chord progression and to an automatic accompaniment performing apparatus.
2. Description of Prior Art
An electronic musical instrument having an automatic accompaniment performing capability is known. A play input device (e.g., musical keyboard) of the musical instrument is used to successively designate chords each represented by a keycode (note number) combination to provide a chord progression. Within the musical instrument there is provided a chord member memory which stores members of each chord in a chord set. Each stored chord member indicates a pitch interval from a chord root. Assuming that one of a plurality of keycodes (note numbers) entered from the keyboard is a root of the chord designated by the plurality of keycodes, a chord root and type determining means converts each entered keycode to a corresponding pitch interval from that root to obtain designated chord member data comparable with that of the chord member memory. The chord root and type determining means identifies a type and root of a designated chord by finding stored chord member data of a particular chord type that matches the designated chord member data. In this manner, there is formed a chord progression in which each chord is represented by a root and a type. The musical instrument further includes an accompaniment pattern memory storing an accompaniment pattern. The accompaniment pattern comprises horizontal (time) component and vertical (pitch) component of an accompaniment line. An accompaniment decoding means converts the stored vertical data to pitch data indicative of an actual pitch of the accompaniment in accordance with an identified chord type and root.
The musical instrument described above has no capability of evaluating a function of a chord in a chord progression. In general, in music, even if a type and root of a chord is known, this is not enough to determine a tonality i.e., a pitch class set available in the time interval of that chord. By way of example, take up a chord of C major (root=C, type=major) having members of C, E and G. If C major chord has a function of tonic (I), a desired set of pitch classes are C, D, E, F, G, A and B which form an ionian scale in a key of C. If same chord has a function of dominant (V), a set of pitch classes C, D, E, F, G, A and B.sub..music-flat. forming a mixolydian scale in key F may be suitable. In the case when C major chord has a function of subdominant (IV), a desired set of pitch classes will be C, D, E, F.music-sharp., G, A and B which form a lydian scale in key G. As noted, it is a nature of music that a specified function as well as specified type and root of a chord is required to determine a desired pitch class set (tonality). Nevertheless, this is disregarded in the musical instrument stated above which instead decodes the stored accompaniment pattern by using only a chord root and type to determine accompaniment pitches. The resultant accompaniment can sound unnatural because of undesirable pitches contained therein that weaken or damage the desired tonality. This may be avoided by restricting vertical contents of the accompaniment to, for example, chord member pitches only. This solution, however, will deprive the accompaniment of musical interest because of its poor pitch contents.
To save storage capacity, a typical prior art automatic accompaniment performing apparatus employs an accompaniment pattern memory which stores an accompaniment pattern only for a single reference chord having a reference root (e.g., C) and a reference type (e.g., major). Typically, vertical pattern element (pitch data) of the stored accompaniment pattern is designed to represent a pitch interval from a chord root. In operation, the pitch interval is modified depending on a detected chord type. Suppose, for example, that the stored accompaniment pattern is written for a chord of C major and includes a pitch data item indicative of a pitch interval of major third from a chord root. If a detected chord type is minor, this pitch data item is lowered by a half tone, thus indicating a minor third from a root. The pitch data item modified by a detected chord type is further modified by a detected chord root to provide an actual pitch in the accompaniment. For a detected root of C, the actual pitch will be E.music-flat. which is minor third degree from the root C. If the detected root is G, the actual accompaniment pitch will be B.music-flat. which is minor third degree from the root G. Therefore, the prior art apparatus of this type has a problem that the pitch line of the accompaniment will change in substantially parallel to the root pitch progression in the chord progression.
U.S. patent application Ser. No. 07/290,295, filed on Dec. 22, 1988, now U.S. Pat. No. 5,003,860, and assigned to the same assignee as the present application discloses a tonality determining apparatus which determines a tonality from a chord progression and an automatic accompaniment performing apparatus which uses the results from the tonality determining means to play an accompaniment. This tonality determining apparatus uses algorithms (programs) rather than data to realize musical knowledge required for determining a tonality. Because of its principles, the tonality determining apparatus provides a tonality with a relatively low reliability. In other words, to obtain an accurate tonality, the tonality determining apparatus of this type would require complicated logic and arithmetic operations consuming a considerable time which would not be permissible in real-time applications such as automatic accompaniment performing apparatus.
Another example of tonality determining apparatus and automatic accompaniment performing apparatus is disclosed in Japanese patent application laid open to public as Kokai Hei2-29787. This tonality determining apparatus searches from a given chord progression for a portion indicative of a specific chord pattern having a particular chord type pattern and a particular chord root difference pattern to determine a key. However, the tonality determining apparatus will never use or reference a key determined already for a preceding portion of the chord progression to determine a key for a succeeding chord in the chord progression. This tends to introduce a delay in detecting a modulation (change of key), resulting in wrong key determination for a portion of the chord progression. Thus, an automatic accompaniment performing apparatus, which is an application of such tonality determining apparatus, cannot hope to perform a satisfactory accompaniment for the reasons stated before.
The automatic accompaniment performing apparatus of the above Japanese patent application Kokai Hei2-29787 includes means for determining a scale from a tonality (from the tonality determining apparatus) and a chord (from a chord progression input device), and an accompaniment pattern memory for storing a plurality of accompaniment patterns each provided for a different one of a plurality of scales. Each accompaniment pattern has a pattern of pitch intervals each from a chord root. In operation, the automatic accompaniment performing apparatus selects and reads from the accompaniment pattern memory an accompaniment pattern corresponding to a determined scale. Then, the apparatus adds a chord root from the chord progression input device to a pitch interval data item in the selected accompaniment pattern to thereby produce a pitch signal of an actual accompaniment tone. Therefore, the automatic accompaniment performing apparatus of this type requires a complicated accompaniment forming system; the accompaniment pattern memory must be provided with a large number of accompaniment patterns written in different keys, imposing a burden on a pattern writer or designer who writes such patterns.